Thank you so much! I know I had seen it somewhere, but then could not remember where exactly. I ordered the book straight away. Unfortunately, being myself new to this kind of repertoire, I can't be of any help concerning other sources for voice and guitar. There is some music under "scores" on this site though.
A performing edition of this was published by Editions Chanterelle in 1997. It is useable but don't believe everything you read in the introduction. The manuscript has never been published in facsimile. I have a photocopy of part of it. Monica